A fluoropolymer having a saturated cyclic structure in its main chain is amorphous and has been known to be a transparent fluoropolymer. Such a transparent fluoropolymer has been used as a transparent coating material, optical material, etc. (JP-A-3-39963 and JP-A-3-67262). Further, a substantially linear fluoropolymer containing hydrogen in its main chain (JP-A-2001-330943) and a polymer containing perfluoro-1,3-dioxol or the like (WO2001/37044) has been known to be highly transparent in the ultraviolet region. Such materials have been applied to e.g. a pellicle material.
A pellicle is, in photolithography as one process in production of a semiconductor device or a liquid crystal display panel, a protective film to be mounted on a pattern of a mask to prevent foreign substances from getting on a photo mask or a reticle (hereinafter they will generically be referred to as mask), thereby to prevent pattern defect at the time of exposure. Usually, a pellicle has such a structure that a transparent thin membrane attached to a frame by means of an adhesive, is disposed on a mask with a certain distance from the mask surface.
In the filed of production of a semiconductor device and a liquid crystal display panel, in which such a pellicle is used, as the wiring and the wiring distance become fine progressively, the wavelength of a light source to be used becomes short rapidly in photolithography also. In recent years, a KrF excimer laser has been introduced for wiring processing with a minimum pattern dimension of at most 0.3 μm. The oscillation wavelength thereof is 248 nm, and a conventional nitrocellulose type membrane material is insufficient in durability. Thus, an amorphous perfluoropolymer as disclosed in e.g. JP-A-3-39963 has been found to be useful as a membrane material.